The present invention relates to a flasher type fish sonar in which a light conductor is rotated by a motor, a luminous body is fixed on a circuit board and an emitted light of the luminous body is emitted through a slit of the light conductor.
In a prior flasher type fish sonar, a circular window is formed in the periphery of a display board provided at the front of a case, the luminous body mounted on a rotary disk is arranged opposite to the window, and the rotary disk is rotated by a motor. Also, brushes are in contact with slip rings provided with the rotary shaft of the rotary disk, an input circuit is connected to the brushes and a flasher display is constituted by the rotary disk and luminous body. The input circuit is connected to a transmitting-receiving circuit of a fish sonar. When a signal from the transmitting-receiving circuit is input from the input circuit to the luminous body through the brushes and the slip rings, an upper portion of the rotary disk becomes a starting point showing the surface of the sea, fish are shown in parts emitted by a rotary timing of the luminous body, and the sea bottom is shown in a part near the starting point.
In the prior flasher type fish sonar, however, when the rotary disk having the luminous body is rotated by the motor, digital signals are input from the transmitting-receiving circuit to the input circuit, and the digital signals are supplied from the input circuit to the luminous body through the brushes and the slip rings. However, the lifetime of the brushes and the slip rings becomes short by the wear of the brushes and the slip rings. As a result, the electric current input into the luminous body is changed, because the contact resistance of the brushes and slip rings is changed by the contact wear and the luminosity of luminous body is changed. Thus, the luminosity of the luminous body is not visible, and the luminosity of the fish in the sea is confused with the luminosity of the bottom of the sea when the change of the luminosity of the luminous body becomes large.